PROCESS FOR PRODUCING ENDCAPPED, LIQUID SILOXANES FROM SILICONE WASTES

Abstract

Process for producing endcapped, liquid siloxanes having chain lengths of greater than 3 silicon atoms from end-of-life silicones, especially from silicone elastomers and/or silicone rubbers, by acid-catalysed depolymerization thereof in a solvent-free reaction system comprising at least one compound providing end groups M.sup.R, at least one compound providing D units, and at least one Brønsted acid.

Claims

1-13. (canceled)

14. A process for producing endcapped, liquid siloxanes having chain lengths of greater than 3 silicon atoms from a silicone waste, by acid-catalysed depolymerization thereof in a solvent-free reaction system comprising: (i) at least one compound providing end groups M.sup.R; (ii) at least one compound providing D units; and (iii) at least one Brønsted acid.

15. The process of claim 14, wherein the silicone waste comprises silicone elastomers and/or silicone rubbers.

16. The process of claim 14, wherein the compound providing end groups M.sup.R and/or providing D units is selected from the group consisting of: hexamethyldisiloxane, polydimethylsiloxanes, poly(methylhydrogen)siloxane, poly(methylhydrogen)polydimethylsiloxane copolymer, trimethylchlorosilane, dimethyldichlorosilane, dichlorotetramethyldisiloxane, α,ω-dichloropolydimethylsiloxane, monoalkoxytrimethylsilane, dialkoxydimethylsilane, α,ω-dialkoxypolydimethylsiloxanes, tetramethyldisiloxane, α,ω-dihydrogenpolydimethylsiloxanes, divinyltetramethyldisiloxane, α,ω-divinylpolydimethylsiloxanes and mixtures thereof.

17. The process of claim 16, wherein said compound provides end groups M.sup.R.

18. The process of claim 14, wherein the compound providing end groups M.sup.R is selected from the group consisting of: monomethoxytrimethylsilane, monoethoxytrimethylsilane, dimethoxydimethylsilane diethoxydimethylsilane, α,ω-dimethoxypolydimethylsiloxanes and α,ω-diethoxypolydimethylsiloxanes.

19. The process of claim 14, wherein the compound providing D units is a cyclosiloxane selected from the group consisting of: hexamethylcyclotrisiloxane; octamethylcyclotetrasiloxane; decamethylcyclopentasiloxane; and dodecamethylcyclohexasiloxane.

20. The process of claim 17, wherein the compound providing D units is a cyclosiloxane selected from the group consisting of: hexamethylcyclotrisiloxane; octamethylcyclotetrasiloxane; decamethylcyclopentasiloxane; and dodecamethylcyclohexasiloxane.

21. The process of claim 14, wherein the acid-catalysed, solvent-free depolymerization of the silicone waste is carried out in a reactor having a volume of at least 5 litres.

22. The process of claim 21, wherein the reactor has a volume of not more than 500,000 litres.

23. The process of claim 14, wherein the acid-catalysed, solvent-free depolymerization of silicone waste is performed in the temperature range of 30° C. to 150° C.

24. The process of claim 14, wherein, when using a compound providing end groups M.sup.R selected from tetramethyldisiloxane and/or α,ω-dihydrogenpolydimethylsiloxanes, the acid-catalysed, solvent-free depolymerization is performed in the temperature range of 35° C. to 80° C.

25. The process of claim 14, wherein the Brønsted acid is employed in amounts of 0.05 to 3 percent by weight, based on the total silicone content of the reaction system.

26. The process of claim 14, wherein the Brønsted acid is a protic acid having a pK.sub.A of less than −1.30.

27. The process of claim 14, wherein the Brønsted acid is a protic acid having a pK.sub.A of less than −4.90.

28. The process of claim 14 wherein the Brønsted acid is selected from the group consisting of: nitric acid, methanesulfonic acid; p-toluenesulfonic acid; sulfuric acid, heptafluoropropanesulfonic acid; pentafluoroethanesulfonic acid; trifluoromethanesulfonic acid; perchloric acid; chlorosulfonic acid; and sulfonic acid- or perfluoroalkylsulfonic acid-acidified ion-exchange resins.

29. The process of claim 14, wherein the acid-catalysed, solvent-free depolymerization of the silicone wastes is performed at standard pressure (1013 hPa).

30. The process of claim 14, wherein the silicone waste comprises silicone adhesives and/or silicone sealants.

31. The process of claim 14, wherein the endcapped, liquid siloxanes comprise alkoxysiloxanes, hydrogensiloxanes, chlorosiloxanes, polydimethylsiloxanes and/or vinylsiloxanes having chain lengths of greater than 3 silicon atoms.

32. The process of claim 14, wherein the process utilizes silicone-contaminated polyolefin wastes, for providing acidic alkoxysilanes, hydrogensiloxanes, chlorosiloxanes, polydimethylsiloxanes and/or vinylsiloxanes having chain lengths of greater than 3 silicon atoms in the course of substantially single stream recovery of the polyolefin.

33. Endcapped, acidic liquid siloxanes having chain lengths of greater than 3 silicon atoms produced by the process of claim 14.

Description

EXAMPLES

[0098] The examples that follow serve solely to elucidate this invention to those skilled in the art and do not constitute any restriction at all of the claimed process. The determination of water contents according to the invention is performed in principle by the Karl Fischer method based on DIN 51777, DGF E-III 10 and DGF C-III 13a. .sup.29Si-NMR spectroscopy was used for reaction monitoring in all examples.

[0099] In the context of the present invention the .sup.29Si NMR samples are analysed at a measurement frequency of 79.49 MHz in a Bruker Avance III spectrometer equipped with a 287430 probe head with slit width of 10 mm, at 22° C. in CDCl.sub.3 solution, and against a tetramethylsilane (TMS) external standard [δ(.sup.29Si)=0.0 ppm].

[0100] The gas chromatograms are recorded on an Agilent Technologies GC 7890B GC instrument fitted with an HP-1 column having dimensions of 30 m×0.32 mm ID×0.25 μm dF (Agilent Technologies No. 19091Z-413E) using hydrogen as a carrier gas and employing the following parameters:

[0101] Detector: FID; 310° C.

[0102] Injector: Split; 290° C.

[0103] Mode: constant flow, 2 ml/min

[0104] Temperature program: 60° C. at 8° C./min-150° C. at 40° C./min-300° C. 10 min.

Example 1 (Inventive)

[0105] Production of a Polydimethylsiloxane from Silicone Caulk

[0106] 30 g of a silicone caulk bead (MEM® Universal-Silikon (white)) discharged onto a polyethylene film and cured, in the form of irregular chunks of 3-4 mm in size, was initially charged with slow stirring into a 500 mL four-necked round bottom flask fitted with a KPG stirrer and a reflux condenser together with 70 g of decamethylcyclopentasiloxane and 12.5 g of hexamethyldisiloxane and then admixed with 0.69 g of concentrated sulfuric acid (0.6 percent by weight based on the total batch) and heated to 120° C. for 4 hours with further stirring.

[0107] Over the course of the reaction the chunk-like constituents of the reaction matrix are gradually liquefied to obtain a slightly viscous liquid comprising only fine solids particles.

[0108] After filtration through a filter press (K 300 filter disk) a .sup.29Si-NMR spectrum of the clear filtrate verifies that a trimethylsilyl-endcapped polydimethylsiloxane has been formed.

Example 2 (Inventive)

[0109] Production of an α-Monochloropolydimethylsiloxane

[0110] 30 g of a silicone caulk bead (Soudal Sanitär Dusche & Bad, transparent) discharged onto a polyethylene film and cured, in the form of irregular chunks of 3-4 mm in size, was initially charged with slow stirring into a 500 mL four-necked round bottom flask fitted with a KPG stirrer and a reflux condenser together with 60 g of decamethylcyclopentasiloxane and 10.0 g of trimethylchlorosilane and then admixed with 0.20 g of concentrated trifluoromethanesulfonic acid (0.2 percent by weight based on the total batch) and heated to 50° C. for 4 hours with further stirring.

[0111] Over the course of the reaction the chunk-like constituents of the reaction matrix are gradually liquefied to obtain a slightly viscous liquid comprising only fine solids particles. After filtration through a filter press (K 300 filter disk) a .sup.29Si-NMR spectrum of the clear filtrate verifies that a mixed chlorotrimethylsilyl-endcapped polydimethylsiloxane has been formed.

Example 3 (Inventive)

[0112] Production of an α,ω-Dihydrogenpolydimethylsiloxane

[0113] 30 g of a silicone caulk bead (Soudal Sanitär Dusche & Bad, transparent) discharged onto a polyethylene film and cured, in the form of irregular chunks of 3-4 mm in size, was initially charged with slow stirring into a 500 mL four-necked round bottom flask fitted with a KPG stirrer and a reflux cooler together with 40.0 g of decamethylcyclopentasiloxane and 30.0 g of an α,ω-dihydrogenpolydimethylsiloxane (SiH value: 3.06 mol SiH/kg determined by gas volumetry (decomposition of a weighed-in aliquot with sodium butoxide solution using a gas burette) corresponding to an average chain length N=9.3) and then admixed with 0.20 g of concentrated trifluoromethanesulfonic acid (0.2 percent by weight based on the total batch) and heated to 50° C. for 2 hours with further stirring.

[0114] Over the course of the reaction the chunk-like constituents of the reaction matrix are gradually liquefied to obtain an H.sub.2S-smelling liquid comprising only fine solids particles which is freed of the solids content using a filter press (K 300 filter disc). The obtained clear filtrate is identified by the corresponding .sup.29Si-NMR spectrum as having the structure of an α,ω-dihydrogenpolydimethylsiloxane having an average chain length N of about 28.7. An accompanying gas volumetric determination on a weighed-in filtrate sample verifies that all SiH employed is retained.

Example 4 (Inventive)

[0115] Production of an α,ω-Dichloropolydimethylsiloxane

[0116] 30 g of a silicone caulk bead (Soudal Sanitär Dusche & Bad, transparent) discharged onto a polyethylene film and cured, in the form of irregular chunks of 3-4 mm in size, was initially charged with slow stirring into a 500 mL four-necked round bottom flask fitted with a KPG stirrer and a reflux condenser together with 40.0 g of decamethylcyclopentasiloxane and 30.0 g of an α,ω-dichloropolydimethylsiloxane (acid value: 4.32 mol/kg determined by acidimetric titration of an aliquot decomposed in H.sub.2O/acetone, corresponding to an average chain length N=5.5) and then admixed with 0.60 g of concentrated sulfuric acid (0.6 percent by weight based on the total batch) and heated to 120° C. for 4 hours with further stirring.

[0117] Over the course of the reaction the chunk-like constituents of the reaction matrix are gradually liquefied to obtain a liquid comprising only fine solids particles which after filtration through a K 300 filter disc affords a clear filtrate which is identified by the corresponding .sup.29Si-NMR spectrum as having the structure of an α,ω-dichloropolydimethylsiloxane having an average chain length N of about 38.3.

Example 5 (Inventive)

[0118] Production of an α,ω-Diethoxypolydimethylsiloxane

[0119] 30 g of a silicone caulk bead (Soudal Sanitär Dusche & Bad, transparent) discharged onto a polyethylene film and cured, in the form of irregular chunks of 3-4 mm in size, was initially charged with slow stirring into a 500 mL four-necked round bottom flask fitted with a KPG stirrer and a reflux condenser together with 70.0 g of decamethylcyclopentasiloxane and 12.5 g of diethoxydimethylsilane and then admixed with 0.69 g of concentrated sulfuric acid (0.6 percent by weight based on the total batch) and heated to 120° C. for 4 hours with further stirring.

[0120] Over the course of the reaction the chunk-like constituents of the reaction matrix are gradually liquefied to obtain a liquid comprising fine solids particles which after filtration through a K 300 filter disc affords a clear filtrate which is identified by the corresponding .sup.29Si-NMR spectrum as having the structure of an α,ω-diethoxypolydimethylsiloxane having an average chain length N of about 20.7.

Example 6 (Inventive)

[0121] Production of an α,ω-Diethoxypolydimethylsiloxane

[0122] 30 g of a silicone caulk bead (MEM® Universal-Silikon (white)) discharged onto a polyethylene film and cured, in the form of irregular chunks of 3-4 mm in size, was initially charged with slow stirring into a 500 mL four-necked round bottom flask fitted with a KPG stirrer and a reflux condenser together with 70.0 g of decamethylcyclopentasiloxane and 12.5 g of diethoxydimethylsilane and then admixed with 0.69 g of concentrated sulfuric acid (0.6 percent by weight based on the total batch) and heated to 120° C. for 4 hours with further stirring.

[0123] Over the course of the reaction the chunk-like constituents of the reaction matrix are gradually liquefied to obtain a liquid comprising only fine solids particles. Filtration through a K 300 filter disc in a filter press affords a clear filtrate which is identified by the corresponding .sup.29Si-NMR spectrum as having the structure of an α,ω-diethoxypolydimethylsiloxane having an average chain length N of about 22.8. A very clear signal is also apparent at a chemical shift about 67 ppm indicating the presence of T groups in an amount of about 0.1 mole percent.

Example 7 (Non-Inventive)

[0124] Attempted Production of an α,ω-Dihydrogenpolydimethylsiloxane

[0125] 30 g of a silicone caulk bead (Hellweg Basic Silikon, transparent) discharged onto a polyethylene film and cured, in the form of irregular chunks of 3-4 mm in size, was initially charged with slow stirring into a 500 mL four-necked round bottom flask fitted with a KPG stirrer and a reflux condenser together with 70.0 g of isopropanol and 12.5 g of an α,ω-dihydrogenpolydimethylsiloxane (SiH value: 3.06 mol SiH/kg determined by gas volumetry (decomposition of a weighed-in aliquot with sodium butoxide solution using a gas burette) corresponding to an average chain length N=9.3) and then admixed with 0.20 g of concentrated trifluoromethanesulfonic acid (0.2 percent by weight based on the total batch) and initially heated at 22° C. for 2 hours initially and then heated to 50° C. for 4 hours with further stirring.

[0126] The chunk-like constituents of the flask contents do not undergo any visible change during this treatment. Cooling the overall mass results in isolation of flask contents where a transparent, colorless liquid phase covers the visually unchanged silicone chunks.

Example 8 (Inventive)

[0127] Production of a Polydimethylsiloxane from Silicone Caulk

[0128] 30 g of a silicone caulk bead (Hellweg Basic Silikon, transparent) discharged onto a polyethylene film and cured, in the form of irregular chunks of 3-4 mm in size, was initially charged with slow stirring into a 500 mL four-necked round bottom flask fitted with a KPG stirrer and a reflux condenser together with 70 g of decamethylcyclopentasiloxane and 12.5 g of hexamethyldisiloxane and then admixed with 0.69 g of methanesulfonic acid (0.6 percent by weight based on the total batch) and heated to 120° C. for 4 hours with further stirring.

[0129] Over the course of the reaction the chunk-like constituents of the reaction matrix are gradually liquefied to obtain a slightly viscous liquid comprising only fine solids particles.

[0130] After filtration through a filter press (K 300 filter disk) a .sup.29Si-NMR spectrum of the clear filtrate verifies that a trimethylsilyl-endcapped polydimethylsiloxane has been formed.